A 7-month-old, paially immunized child presented with cough ending in characteristic whoop. Which of the following is considered the best type of specimen to isolate the organism and confirm the diagnosis
**Core Concept**
The question is testing the ability to identify the best specimen for isolating the causative agent of pertussis, a highly contagious respiratory infection caused by *Bordetella pertussis*. This bacterium is known for its characteristic "whooping" cough.
**Why the Correct Answer is Right**
The best specimen for diagnosing pertussis is the nasopharyngeal swab (NPS), as it directly samples the site of infection. This method is more sensitive than throat swabs, which may be contaminated with normal flora. The NPS can be collected at any stage of the disease, including the catarrhal and paroxysmal phases. The specimen should be transported to the laboratory immediately and cultured on Bordet-Gengou agar, a selective medium that allows *B. pertussis* to grow.
**Why Each Wrong Option is Incorrect**
* **Option A:** A throat swab is less sensitive than a nasopharyngeal swab due to the presence of normal flora that can contaminate the sample.
* **Option B:** A blood culture is not the best specimen for diagnosing pertussis, as the bacterium is primarily a respiratory pathogen.
* **Option D:** A stool sample is not typically used for diagnosing pertussis, as the bacterium is not shed in the stool.
**Clinical Pearl / High-Yield Fact**
Pertussis is a highly contagious disease that can be prevented with vaccination, but immunization rates remain low in some regions. The characteristic "whoop" is often absent in infants and young children, making diagnosis more challenging.
**Correct Answer:** C. Nasopharyngeal swab